JKL issues Area Forecast Discussion (AFD) at Aug 8, 4:39 PM EDT
583
FXUS63 KJKL 082039
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
439 PM EDT Thu Aug 8 2024
.KEY MESSAGES...
- Showers and thunderstorms will affect a few locations this
evening and on Friday, but most places will be dry.
- Much cooler and drier air will arrive as we move into the
weekend and carry into early next week.
- A small potential for showers and thunderstorms returns around
the middle of next week.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 439 PM EDT THU AUG 8 2024
Tropical Storm Debby is accelerating northward through the
Carolinas late today, and we continue to be on the fringe of its
influence. There's been enough heating to fire up some isolated
showers. There hasn't been any lightning yet, but it can't be
ruled out. Will again look for activity to die out as instability
wanes this evening. The deep moisture and solid precip shield is
further to the east and southeast and models now suggest it will
not quite make it west into KY. However, high clouds associated
with the system will persist into the night. As high clouds begin
to thin out eventually, there is also a likelihood of low clouds
developing overnight as our low level flow backs to the northwest
and becomes upslope in cold air advection when Debby departs. If
low clouds don't become prominent, there will be a good potential
for fog development in the deepest valleys. However, the issue of
low clouds vs. fog is uncertain.
Low clouds and/or fog will lift and break up on Friday as heating
occurs. Forecast sounding still show some potential for a few
showers or thunderstorms to develop around mid day or early
afternoon over extreme eastern KY after some heating. As drier air
low level air makes its way in, these should dry up later in the
day.
That will leave mainly clear skies and good radiating conditions
on Friday night. Cold air advection will continue, but flow will
be weak and most valleys will probably decouple from the flow.
This would allow min temps to drop into the 50s for most places.
.LONG TERM...(Saturday through Thursday)
Issued at 420 PM EDT THU AUG 8 2024
A relatively uneventful and dare we say - pleasant - extended
forecast period is in the works.
By 12Z Saturday, a strong upper level low will be in place across
southern Ontario, just north of Lake Superior. This will create a
large-scale trough across much of the northeastern Conus,
encompassing the Ohio Valley. The upper level low will slowly
progress eastward, finally reaching New England by late Monday...but
keeping much of the Ohio Valley in this continued troughing pattern
with NW to SE flow. Models start to diverge heading into next week,
with the ECWMF bringing another low and shortwave through the trough
flow and into the Ohio Valley late Monday into Tuesday. Can't rule
out another disturbance developing and moving through this flow
later in the week. Overall, with a strong high pressure ridge in
control across the southern Conus, and the upper level low in place
to our northeast, this NW to SE flow will remain throughout the
period.
The nice thing about this flow is that it will advect cooler and
drier air into the region. This also means less instability and
humidity, so less likely for afternoon diurnally driven convection
from mixing alone. Despite the strong upper level system and
associated surface low pressure system in southern Ontario, most of
the moisture from this system will be confined well to our north.
This leaves the Commonwealth dry. In fact, according to the NBM, we
should remain dry through the weekend and well into the start of
next week. The next chance for rain across the CWA according to the
NBM isn't til Wednesday and Thursday. This seems to be tapping into
the GFS bringing a shortwave through the region. That being said,
each model has precip moving through the CWA via an upper level
disturbance/shortwave throughout the entire extended period, but
none of them agree. It is likely that the NBM is averaging the
precip potential out on the days it claims we are "dry", and that
the models are continuing to change course with each run. So while
the forecast is currently dry, can't completely put faith that this
won't change over the coming days.
With this in mind, on Thursday both the GFS and ECWMF show a system
moving across the state. The GFS is quite robust with the rainfall
potential, including some high QPF. This is reflected in the WPC
QPF, but the NBM didn't pick up on the high pops just yet. The
result is a bit of a mismatch in the forecast grids, with only
slight chance pops and QPF over 1/3". Hoping that this discrepancy
begins to work itself out in the coming model runs and forecasts.
As was noted above, the one perk of the NW flow regime is the
advection of a cooler and less humid airmass. Highs on Saturday will
only top out in the upper 70s and low 80s. This will persist through
the start of the work week. Eventually temperatures will begin to
modify warmer with continued sunshine, so some low to mid 80s are on
tap for Tuesday onwards. However, humidity should trend lower
outside of any precip chances.
&&
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 137 PM EDT THU AUG 8 2024
Mainly VFR conditions are forecast until late tonight. Isolated
showers or thunderstorms will affect some locations this afternoon
and evening, but the probability at any TAF site is too low at any
given time to be addressed directly. MVFR or worse conditions due
to a combination of fog and low clouds are expected to develop
overnight an last through early Friday morning for most places.
VFR conditions should return area wide early Friday afternoon.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...HAL
LONG TERM...JMW
AVIATION...HAL
Source: JKL issues Area Forecast Discussion (AFD) at Aug 8, 4:39 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202408082039-KJKL-FXUS63-AFDJKL)
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